Conduction mechanism and 1/f noise in ZnO varistors

Abstract
The conduction mechanism in ZnO varistors has been studied assuming thermionic emission as the only way of charge transport. A model elaborated on that basis has been satisfactorily applied to the approximation of the IU and CU characteristics and has made it possible to determine the barrier height Φb(300 K)=0.86 V, the donor concentration ND≂1019 cm3, the effective number of grains between the electrodes g≂20, the position of the Fermi level ECEF≂0.07 eV, and the donor level ECED≂0.20 eV. The relative power spectral density of 1/f current fluctuations SI/I2 in the varistors in the ohmic region has been calculated, starting from the mobility fluctuation approach of the 1/f noise. The calculated linear relationship between SI/I2 and the varistor resistance in the ohmic region has been confirmed by the experimental results. The calculated 1/f noise density is in agreement with the observed density.

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